HMP Perth has been named Scotland’s most violent prison, with staff forced to deal with at least one serious assault every four weeks.

A new study has revealed that the rate of attacks has soared to a five year high at the Tayside jail.

There have been 13 serious assaults or brawls in the last 12 months, compared with just seven the year before.

The country’s biggest jail Barlinnie — where the population of 1,600 is well over double the amount in Perth — only recorded six incidents over the 2015/16 period.

Politicians have called for an inquiry into the latest study, which was released by the Scottish Prison Service following a freedom of information request.

Local MSP Murdo Fraser said: “The increasing number of serious assaults at Perth Prison is a real cause for concern.

“While assaults in other prisons across the country have remained stable and in some instances are reducing it would appear as though they are rising fast in Perth.”

He added: “The safety of prisoners and prison staff is paramount and I would hope that the prison service is able to provide answers as to why 2015/16 has been so violent inside HMP Perth.”

Earlier this summer, police in riot gear were scrambled to the Edinburgh Road compound after two inmates attacked staff and set fire to a pool table.

Other prisoners were evacuated when convicted killer Kristopher Marshall and fellow inmate Ronald Smith staged a stand-off in the jail’s C Hall. The incident cost tax-payers an estimated £40,000.

The pair were later sentenced to a further four years behind bars.

Incidents at Perth Prison have also skewed local police records, which suggested a massive surge in violence across the city.

Recent city centre figures from Police Scotland showed that serious assaults in Perth had rocketed by more than 150%.

But chief superintendent Eddie Smith said the figures were weighed by crimes recorded at the jail.

He told a meeting of Perth and Kinross Council’s community safety committee: “We have seen an increase in the number of serious assaults at the prison.

“We continue to work with serious management there to see what assistance we can provide and if there’s any operations that would help.”

A prison service spokeswoman declined to comment directly on the rising numbers at Perth Prison. She said: “We recognise the importance of providing a safe and secure environment for our staff, those in our care and visitors.

“Serious assaults are routinely reported to the police.”

The second highest tally of serious assaults (10) was recorded at Polmont Young Offenders institute and Low Moss, which each hold a similar number of prisoners as Perth.

Scotland’s newest prison, HMP Grampian which opened at Peterhead three years ago, had five assaults in the last 12 months.

There were no such incidents at open estate Castle Huntly, near Dundee, and just four recorded at HMP Glenochil in Alloa.